It was likely left behind by one of the many jihadist groups now training in the USA and Canada. There was one group in Washington State.Another one in upstate New York, Islamberg.
The miitary did not likely drop it, these things are COUNTED
repeatedly if removed from arsenal.
The serial numbers will tell the tale.But will we ever know? Unlikely.
My bet is that it was stolen from a US military installation, but it is strange to be found near a Canadian Naval base.Another jihadi training run? THe Canadian Navy has no use for these, I doubt there are any on the base.
About the most useful thing I find by the side of the road are wheel weights. Harumph!